During the operation of an internal combustion engine, in particular an internal combustion engine for driving high-performance motor vehicles, very high temperatures, sometimes exceeding 1000° C., can arise at the exhaust-gas side. Suitable measures must be implemented to prevent thermal damage to components provided in the exhaust tract, in particular close-coupled exhaust-gas catalytic converters, turbines of an exhaust-gas turbocharger or exhaust-gas probes.
DE 102 01 465 B4 discloses a method for controlling a component protection function for an exhaust-gas catalytic converter of an internal combustion engine having an engine controller which contains an exhaust-gas temperature model.
The exhaust-gas temperature model has a characteristic curve which represents an influencing factor on the exhaust-gas model temperature as a function of the air ratio lambda. An inverse exhaust-gas temperature model is provided, wherein the characteristic curve of the exhaust-gas temperature model is transformed into an inverted characteristic curve for the inverse exhaust-gas temperature model. A lambda setpoint value for the component protection is calculated as an input variable for a lambda coordination on the basis of the inverse exhaust-gas temperature model, wherein a component-critical limit value is used in the inverse temperature model.
DE 10 2004 033 394 B3 describes a method for controlling an internal combustion engine having an engine controller, wherein the engine controller sets the exhaust-gas temperature by means of the air/fuel mixture and has a temperature model which determines, for a component in the exhaust tract, a predicted temperature which will be assumed if the present operating and driving conditions are maintained for a relatively long period of time. For the component protection, the engine controller regulates the exhaust-gas temperature as a function of the predicted temperature.
Furthermore, it is known to replace a naturally aspirated engine with a supercharged engine of smaller swept volume. This so-called downsizing by means of turbocharging leads to a more expedient power-to-weight ratio and therefore a changed load collective, that is to say the operating duration spent in relatively high load ranges increases considerably. To limit associated thermal loading of components (exhaust-gas catalytic converter, exhaust-gas probe, exhaust-gas turbine) arranged in the exhaust tract, it is possible to use-liquid-cooled exhaust manifolds which are partially or even completely integrated into the cylinder head of the internal combustion engine.
DE 10 2007 050 259 A1 describes a supercharged internal combustion engine with integrated exhaust manifold and liquid-type cooling arrangement.
The exhaust-gas temperatures can be reduced through the use of a liquid-cooled exhaust manifold. The liquid-type cooling arrangement may be connected to the general cooling circuit of the internal combustion engine and activated by means of corresponding valves or by means of a pump. Owing to a multiplicity of possible defects of components of said cooling circuit, a failure of the liquid-type cooling arrangement of the exhaust manifold cannot be ruled out. Said failure in turn results in an increase in the exhaust-gas temperature and therefore, under some circumstances, damage to the components at the exhaust-gas side.